1. Field of the Invention
The present invention generally relates to image forming and, more particularly, to an image forming apparatus such as a copying machine and a printer of, for example, an electrophotographic method or an electrostatic storage method.
2. Description of the Related Art
When a color image is formed, an image forming apparatus of an electrophotographic method analyzes print information from an external apparatus, such as a computer, to rasterize image information contained in the print information into image information of each color of yellow, magenta, cyan, and black. Then, after a preparatory operation for image formation is performed based on the image information obtained from the image rasterization, the image forming apparatus successively forms a toner image on a photosensitive drum by toner of yellow, magenta, cyan, and black, and performs a multi-layer transfer of the toner images to an intermediate transfer body or a recording medium.
Thus, the time until an image is formed is affected by the time necessary for the preparatory operation for image formation. Therefore, Japanese Patent Application Laid-Open No. 6-175514 discusses a method for reducing the time necessary for the preparatory operation by controlling the timing to start the preparatory operation.
However, after the preparatory operation is performed, the timing for image formation is set to be able to start the image formation from a front end of the recording medium with reference to the size of a recording medium so that the image formation may be started from anywhere in the recording medium. Thus, there is an issue that if the sizes of recording media are the same, the time necessary for image formation barely changes regardless of whether an image is formed only in a front-end portion of the recording medium or an image is formed only in a backend portion of the recording medium.